In a large-capacity inverter device that drives a motor for a compressor and a fan, etc. of a refrigeration air-conditioning apparatus, a method is used in which a DC busbar voltage for inverter driving is generated by a three-phase full-wave rectifier circuit. In the refrigeration air-conditioning apparatus, in order to increase energy consumption efficiency (COP) during rated cooling and heating operations and full-year energy consumption efficiency (APF) through one year, the motor for the compressor tends to be designed such that an induced voltage (counter-electromotive force) is substantially equal to a power supply voltage at approximately a rotation speed used in rated operation of the refrigeration air-conditioning apparatus. In such a case, when the motor is caused to be operated in a high-speed range exceeding this rotation speed (e.g., during high-load operation), since the inverter device cannot output a voltage equal to or higher than the power supply voltage, the current of the compressor increases due to output voltage saturation, and the efficiency of a converter decreases due to a decrease in motor efficiency and an increase in loss of the inverter device. In addition, the operation range may become narrow depending on the demagnetization resistance of a magnet used in the motor for the compressor and the allowable current and allowable temperature limit of a semiconductor used in the inverter device.
As a countermeasure against these problems, for achieving high-efficiency driving of the motor and expanding the operation range, and for expanding the output voltage range of the inverter device, a power conversion device having a booster circuit has been proposed (see, e.g., Patent Literature 1). Patent Literature 1 proposes an “electric motor driving apparatus characterized in that the DC voltage control means is configured to add a voltage for the amount of change in speed to a predetermined DC voltage command value to be supplied to the voltage conversion circuit, and output the resultant value”. In the electric motor driving apparatus in Patent Literature 1, the predetermined DC voltage command value to be supplied to the voltage conversion circuit is set so as to increase in proportion to a motor rotation speed. Therefore, the electric motor driving apparatus in Patent Literature 1 performs control of optimizing a boost amount of the booster circuit and is able to minimize loss occurring in the booster circuit at each rotation speed, by maintaining the boost amount at a necessary minimum.
In addition, Patent Literature 2 proposes a “control method for a self-excited rectifying device, characterized in that in response to the magnitude of an output value of the DC power measuring means, the carrier frequency of the carrier frequency varying means is increased when the output value is low, and is decreased when the output value is high”. In the control method in Patent Literature 2, by varying the carrier frequency, the elimination ratio of noise current by an LCR filter is changed. With such a configuration, it is possible to improve the total power factor.